Append only files (AOF) in ElastiCache for Redis
By default, the data in a Redis node on ElastiCache resides only in memory and isn't persistent. If a node is rebooted, or if the underlying physical server experiences a hardware failure, the data in the cache is lost.
If you require data durability, you can enable the Redis append-only file feature (AOF). When this feature is enabled, the node writes all of the commands that change cache data to an append-only file. When a node is rebooted and the cache engine starts, the AOF is "replayed." The result is a warm Redis cache with all of the data intact.
AOF is disabled by default. To enable AOF for a cluster running Redis, you must create a
parameter group with the appendonly parameter set to yes. You then assign that
parameter group to your cluster. You can also modify the appendfsync parameter
to control how often Redis writes to the AOF file.
Append-only files (AOF) aren't supported for cache.t1.micro and cache.t2.* nodes. For
nodes of these types, the appendonly parameter value is ignored.
For Multi-AZ replication groups, AOF isn't enabled.
AOF isn't supported on Redis versions 2.8.22 and later.
AOF can't protect against all failure scenarios. For example, if a node fails due to a hardware fault in an underlying physical server, ElastiCache provisions a new node on a different server. In this case, the AOF file is no longer available and can't be used to recover the data. Thus, Redis restarts with a cold cache.
For greater reliability and faster recovery, we recommend that you create one or more read replicas in different Availability Zones for your cluster. Enable Multi-AZ on your replication group instead of using AOF. AOF isn't enabled for Multi-AZ replication groups.
For more information on mitigating failures, see Mitigating Failures when Running Redis.
For more information, see the following:
